Secondary oil recovery by selfpropelled solvent extraction



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PRGPELLED SOLVENT EXTRCTION o u N -r LUNEL der Jr.

2e- VO Y I George: GJEJ BINDER, JR #ATO QATQ'J vm J d. e l. 1Q.. FV

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' naar I Delaware f, i apparati@ January 29,1952, sensi Nnzssss sciame. (ctms-.nf

the recovery of petroleum vfrom underground oil formations.A l'he invention concerns a technique o t secondary recoveryl in which a limitedvolume of a liquefied, normally gaseous, hydrocarbon is injected int an oil-bearing oil has been seriously depleted. After injection of the body of liquid hydrocarbon, the injection well through closed oli. Thereafter, the hydrocarbon is permitted to va porize in the formation in a manner to drive oil through the formation to the producing wells referred to without "necessity for providing any extraneous driving force. The process is thus a secondary recovery method in which a #bank of solvent is moved through an oil reservoir to pro mote oil production under the influence of the propelling force of the vapor pressure oi the injected solvent.

In ,the production of petroleum oil from oil-bearing tr'ity is carried out by so-called"primary production methods. During this phase of production, the energy .ofthe 'reservoir is relied upon to cause production of oil vvrnonly recovered by primary production methods.

methods have been suggested. Secondary recovery methods are designed to augment the remaining reservoir energy after depletion by primary recovery techniques. More cxi which provides'uid access to an oil-bearing stratum penetrated by'one or more producing wells. By injecting the oil-bearing stratum so as to increase the ultimate oil recovery from. producing wells. For some time, water ooding has been one of the practical appjcations of the principles of secondary recovery.

Presently known secondary recovery techniques however leave much to' be desired. it is generally appro ciated that even as best applied, presently known second- -thisconnectiorg as a rule of thumb, it has been stated that when primary production methods produce' about one-third of the available oil, secondary production methods will permit recovery of an additional one-third of the oiL Hencc, about' one-third of the total oil present generally remains in the reservoir and, isnot recovered by presently employed production methods..

- Again', a characteristic of present secondary recovery methods is the inherent expense ofthese' methods. ln

ducingformation, necessitating extensive' uid treating This invention concernsa novel process forl improving stratum penetrated by oil wells from which production oi which the hydrocarbon is introduced to the formation is formations of the earth, the rst phase of production at:-

In the attempt to recover greaterportions of the avail able oil in oil-.bearing formation, secondary recovery j v. plicitly, by way of definition, a secondary recovery method f requires the introduction ofuid through an injection well.

assistanat... en..

' SECONDARY OIL RECOVERY BY SELF- X PRIEILED SOLVENT EXTRACI'ION George G. Binder, Jr., Tulsa, Gkla., assigner .o Esso Research and Engineering Company, n corporation of to provide an improved .technique of secondary recovery permittinggreater ultimate recovery of oil on an eco-z oil-bearing formation.

- substantially all of this volume of solvent 'in liquid form.'

" rates are required.. .f-

' mation. These temperatures are generally inthe range of' from producing wells. It is sometimes stated that about one-thirdof the'total available oil in a formation is comf uid in this manner, it is possible torforcfoil through this connection, it is apparent that the cost o f providing apparatus to injectlarge volumes of uid 'into a pro- Y ont tendsto advance through the oil'so as to drive the oil and pumping installations, otlsets to a considerable degree the value of thc oil recovered thereby. As a practical sure of this limited volume of liquid hydrocarbons as a driving force-for :he production of oil.

" techniques at producing wells penetrating' the oil-bearing each producing well or conversely, that four producing of .liquid propane will .occur to occupy a volume iequivfliatented:Sepia 20,1955'. .f

matter, this limitation requires termination of secondary recovery vtechniques when o production becomes uneconomic; at a time well prior to complete recovery of oil fromagivcn reservoir. t Itis therefore the principal ol'ijcctv of this invention nomical basis. This is achieved by utilizing a limited s. volume of liquefied, normally gaseous, hydrocarbons; the` volume employed is a minor portion of the total hydrocar-bon porc volume of the-reservoir treated. The process is conducted so as'to permit utilization of the vapor pres In accordance with this invention, tht-.reforma limiten amount of a liquefied hydrocarbon is injected into an The volume of the liquefied hy-. drocarbon required ranges from about 10 to 30% of the total porc volume in the formation to be affected by the solvent injection. injection is to be' carried out in a manner to provide introduction into the formation of Towards this end, high injection pressures and injection The hydrocarbon tobe employed as a solvent may broadly be any readily liquefied normally gaseous hydro-'- carbon providing a substantial vapor pressure at the teme peratures ordinarily encounteredin an oil-bearing forabout to, 250 F. although temperatures outside this. range may be encountered. In particular, therefore, thchydrocarbon which may beemployed may constitute a hydrocarbon hat ing from two to five carbon atoms. For a variety o reasons, however, propane is-thc hydrocarbon f best'. adapted for utilization in the process o i this invention, .and Areference will particularly be made hereinafter to the use of propane. By injecting propane into an oil-bearing formation at' a pressure in excess of its vapor pressure at the reservoir conditions, for example, about 500 pounds per square`A inch, it is possible to sure sulliciently rapid penetration i of the propane into the formation so as'to permit-little vaporization of the liquciied propane. Consequently, it is praccal to introduce the requisite volume of liquetied l A propane into an oil-bearing formation so as to .provide the propane in liquid form in. oil-bearing strata adjacent the injection well. Thereafter, it is only necessary to close off the injection weiland to carry out normal producing Astrata. into which the propane has been injected. v Any desired pattern of producing and injection wells. may be employedin the .practice vof this invention. Thus, for example, the so-calle'd live-spot pattern may be cmploycd, if desired. This pattern is such that vfour produc ing wells are equally spaced about a single injection well. Consequently, in an area containing lwells so spaced, it. may be considered that four injection wells encompass wells encompass each injection well. This or other of the generally employed patterns of wells in secondaryrecovery techniques may be used. lAgain, it may be cm; phasized that thespacing of the wells may follow the generalpracti'cc. "1 '#5' The banl; of liquid propane existing in iheformation adjacent the injectionwell is operative to cause oil production in'thc following manner: A concentration gradicnt-may be considered to exist between the liquid propane andoil contained in the porcs of thc reservoir. This gradibefore ittowards the'producngwelln -As the' process continues, vaporimtion of a portion of the original body t c l i Y `aient tothe displacedsolvent provided y pressure of the propane ja given oil reservoir is :it a temperature of about 1203 'The vapor pressure o propane -ction of the reservoir containing v full pressure originally applied is available after the tottlal vapor pressure. Consequently, it. may

ldepending upon the partial to secure effective oil recovery.

l liquid propane'which is injected into a vaporization occurs so as to :substantially maintain the vcorresponding 'tn physical `of the nature providing an oil reservoir.

is such that only a'srnall portion ofthe body need be vaporized to fill the pore original solvent The ad# space of the swept-out portion of the reservoir.

f vauce of the propane-oil concentration gradient referred to is accompanied by an increasingly high oil concentration in the propane-oil mixture. As a result, the partial gradually decreases.

understood by reference be assumed that F.

These principles can well bel n to a. typical reservoir condition. Le! it about 240 pounds per square inch absolute. Consequent- I ly, if the producing wells are being pumped; the pressure drop available to act as a driving force is 225 pounds per l t square inch. As the oil drive proceeds and the available drive pressure drops as indicated, thedrop in driving pressure-which occurs as oil is swept by the propane is oiset in large part by the decreasing length of the porfiowing liquid. rllius, the

at this temperature isk on. The ong'marbody of liquid gas was then blown through the core so as to decrease injection when it is necessary to drive oil over the comresulting diminutionof the partial pressure of the propane v. is otset by the correspondingly shortei length of travel required. In the p; s ,alar case referred to, there would be a i3 fold increase in the volume of propane by the conversion of liquid propane to gaseous propane at tts hydrocarbon pore volumes of propane were initially inpore volume of the core. During injection of the propane be secu that if 0.20

jected into the reservoir, vaporization of 37.5% of the n original banliof`propanc would be sufficient to lill the entire formation with propane gas at itsvapor pressure l "of 240 pounds per 'square inch absolute, Consequently,

it may be appreciated that injection of the stated proportion of liquid propane provides adequate driving force,

As brought out, therefore', secondary recovery in the process of this invention depends upon the vaporization o a portion of a body of formation. This uid maybe introduced through the injection well so as to -force 'and permit recovery of the propane in the reservoir. This is particularly attractive since the propane may be produced and recovered as an essentially uncontaminated gas. ,It is therefore relatively simple to repressure theV propane gas and to cool it for liquefaction and reuse in secondary recoverytoperations.

'the nature of this invention may be appreciated by reference to the. attached drawing which graphically indicates the operationof two secondary recovery operay tions conducted in accordance with this invention.

In order to evaluate the operability ard advantages of experiments were conducted in athe present invention, manner to simulate field conditions. In these experivaporization of the-propane,

the reservoir to producing wells.-

` .pressure of`propane at this temperature. The results,of

the general mechanism of preciably.

of the-propane did not cause loil production but was etico' of the core progressively dropped from 62 pore volume percent to an ultimate ligure of about 18 pore volume ments, -a 4-foot corewas prepared consisting of consolidated sand. A phenol-formaldehyde,plastic was used to consolidate the sand so as to provide a core closely this character it has lbeen established that a core of Athis nature accurately simulates actual conditions of porosity In work ofV properties to a sand -formation t K sofas Ato permit driving i t with provision for periodically determining the nature and cles, it may be noted that the progress of theoperation `shown in the direction of the arrows fprovided. Thus, f

that the plastic employed in. consolidation the position of connate water. This core w'as then arranged uids completely throughjhe core concentration ofiluids present in the core and for determtningthe volume and nature of fluids passing through the core. The equipment was so arranged as to permitl and -to permit release and recovery of fluids from the o'pposite'end of-the core at any desired pressure. The core was two inches in diameter and was sealed in a steel tube- A dluring these operations. 1 i. f i

ln a iirst step oit'he procedure, the core was, saturatedv with a hydrocarbon oil. ln the particular 'experimentsto be described, normal decane was employed. Nitrogen the oil saturation.to a value of of the total pore volume. The core was thus placed in a condition simulat ing that to be expected in an oil-bearing formation partinlly depleted of oil by primary recovery methods.v Thereafter, application'of the process of this invention was initiated. t Y l t Liquid propane was injected to the core ata pressure of 300 pounds per square inch. in one operation, the amount .oi propane injected wa's'equal tolSrof the*V pore volume of the core, while in another operation the amount of'propane injected amounted to 32% of the total and thereafter, the fluid produced'from the opposite end` of the core was recoveredand analyzed. By repetitious analyses conducted. during the operation, determinations were periodically made as t'o the total oil saturation of the core and as to the gas saturation. During these o`perations, the. temperature was maintained at about'75" F. so that the available pressure for driving oil'through the core was about pou-nds per square inch-the vappr these operations are 'represented in the attached drawing in which the oil saturation of the core is plotted against the propane saturation of the'core, each'expressed as aA percent of the total pore volume of the core. -Y y Referring first to the operation indicated by solid ciri may be followed on the graph' by moving along the line starting at -the upper left-hand portion of the drawingL. the core originally contained about 62 pore volume per' cent of oil and consequently about 38 pore volume percent of gas. Propane-was injected as shown by the values of the abscisa until l5 pore `volume percent of liquid 'propane had been introduced. During this period of propane injectiom'V it will be observed thatthevolume pcrcentof. oil contained in the core did not change ap` Consequently, during this period, iniection.

tive to'force the original gas. in part, fromfthe core. Afterthe iniection of liquidpropane, the core was sealed oft' at the endof the core at which the propane was iti-5 jected. Subsequently, as indicated in the graph, this body of liquid propane 'was effective in forcing oil from the core. Thus, it will be observed that the oilsatu'ration percent. lt will also be observed. that' during this' period of oil productiom'little propane was produced with the oil since the propane saturation only changed' from a value of about 15 pore volume percent to about 14 pore f volume percent. i t

At a. later phase in the recovery operation, ol'recovery substantially ceased and substantially pure propane was obtained from the core.. 'lhns as shown bythe lower-t` most portion of the graphical line referred'to, in the last .Y pbase of the operation, oil saturation remained substan- T constant at a value of about 20 pore volume pen 1 percent tosubstantially nil.

which a self-propelled propane drive can operate. ln a first phase of the operation, aboutlO to 30fpore volume g percent of liquid propane is injected, forcing from a reserf voir a small portion of the gas which may be present, butl with substantially no oil production. Thereafter, as diffusional and capillary processes occur, movement of the liquid propane under thedriving force of its own vapor pressure causes production of oil with substantially .no

' portion of the oil present in the reservoir towards producing wells. Finally, after some limitmg value of oil recovered, again driven by the' vapor pressure of the propane.

Since the process of this invention depends inpart upon diffusion, some improvement in recovery` is .obtainable by lengthening the time of operation. 'ln an operation to demonstrate this effect, a back pressure of 90 pounds per square inch was maintained on the core referred to so as to lengthen the period of oil recovery. This pressure was gradually dropped. l't was found that improvement in oil recovery of' about 2.5% was obtainable. This factor must be considered therefore in conjunction with the fact that in actual operation, in spite of a somewhat greater vapor longer times are involved.

Referring now to the operation represented by the open circles of the drawing, an operation is graphically presented in which 32 pore volume percent of propane was employed. nthis case, it will be observed, from the tion of liquid'propane injection, oil production had been initiated.` Again,'how ever, after completion of propane injection, oil production was achieved' with substantially no propane production. Finally, the operation terminated cent while the propane saturation changed from about 14 covery is attained, substantially pure propane may 'oe repressure, much greater distancesand consequently much.

" `gradually downwardly sloping line, that prior to comple,-v

V 'emessa QAM;

This operation-therefore demonstrates the manner in production of propane. This is effective to drive a major I pane gas during the principal portion of production. It I l o nl'y after oil has been driven from the reservoir to pro-r vide an economically practical maximum of oil recovery that propane in any substantial volumes will be produced. This propane may tten be recovcred'in substantially pure 1 form, facilitating repressuriziug and rta-injection of the@V propane as desired. v Whatis claimed is:

volume percent of a liquefied normally gu'eous Cz to hydrocarbon into the reservoir through the said injection well whereby a bank of liquid phase hydrocarbon material will exist in the said formation adjacent-,thc injection well, thereafter discontinuing the injection of said liquefied hydrocarbon, sealing said injcction'well to prevent-release of hydrocarbon material therefrom, and maintaining a. pressure at the said production well and the adjacentformation at a level to permit vaporization of the said liquefied hydrocarbon at-.the temperature of the formation, and

withdrawing fluid from said production well.

2. A process for the secondary recovery of petroleum y.. oil from an oil-bearing formation penetrated by a vfirst well' l Y 'hereinafter referred to as a production well-and a second well hereinafter referred to as an injection weil which comprises the steps of: injecting about l0 to 30 pore Y volume percent of av liquefied normally gaseous C: to Cl hydrocarbon into the reservoir through the said injection well whereby a bank of liquid phase hydrocarbon matel' rial will exist in the said formation adjacent the injection a iinal phase of operation in which'substantially pure propane recovery. was obtained with little additional oil recovery. f The ultimate oil recoveryamounted to about 46 pore volume .percent leaving a vresidual oil content of about 16 pore volume percent.

of this invention is particularly adapted for economical, effective secondary recovery operations. In the practice ofthis invention, it is particularly contemplated that suffiervoir atected by an injection well. Thereafter, by sealing off the injection well so as to maintain the vapor pressure of the propane, and by carrying out normal production operations from the producing wells, effective n'f -covery of oil may be achieved. As demonstrated, the oil i j will Abe recovered substantially uncontaminatedy with pro I As exemplified by these examples therefore, the process n cient propane be injected at an injection well s'o as to providea minor fraction of the total pore volume of a reswell, thereafter discontinuing the injection of said liquefred hydrocarbon, scaling said injection well to prevent4v release of hydrocarbon material therefrom, and mantaininga pressure at the said production well and the adjacent formation at 'a level to permit vaporization of the..

saidliquetied hydrocarbon at thetempcratu're of the for* mation, withdrawing petroleum oil from said 'production well until substantial proportions-"of thesaid Cz to Cs hydrocarbon reaches the production well, thereafter injecting an inert iluid at the said inject-ion well and 'recovering the said Cz to C5 hydrocarbon from the production well. Y'

3. A- process as defined by claim l wherein said liquefied normally gaseous hydrocarbon comprises propane.

RefcrenceszCited in the lc of this patent l UNITED STATES PATENTS wright June 3'0, 1914 Campbell Ian. 1.2, 1943 Buddrus et al. a Dec. 17, 1946 Nelly, Ir. Jan. 8,' 1952 Brownscombe Sept. 2, 1952 

1. PROCESS FOR THE SECONDARY RECOVERY OF PETROLEUM OIL FROM AN OIL-BEARING FORMATION PENETRATED BY A FIRST WELL HEREINAFTER REFERRED TO AS A PRODUCTION WELL AND A SECOND WELL HEREINAFTER REFERRED TO AS THE INJECTION WELL WHICH COMPRISES THE STEPS OF INJECTING ABOUT 10 TO 30 PORE VOLUME PERCENT OF A LIQUIFIED NORMALLY GASEOUS C2 TO C5 HYDROCARBON INTO THE RESERVOIR THROUGH THE SAID INJECTION WELL WHEREBY A BANK OF LIQUID PHASE HYDROCARBON MATERIAL WILL EXIST IN THE SAID FORMATION ADJACENT THE INJECTION WELL, THEREAFTER DISCONTINUING THE INJECTION OF SAID LIQUEFIED HYDROCARBON, SEALING SAID INJECTION TO PREVENT RELEASE OF HYDROCARBON MATERIAL THEREFROM, AND MAINTAINING A PRESSURE AT THE SAID PRODUCTION WELL AND THE ADJACENT FORMATION AT A LEVEL TO PERMIT VAPORIZATION OF THE SAID LIQUEFIED HYDROCARBON AT THE TEMPERATURE OF THE FORMATION, AND WITHDRAWING FLUID FROM SAID PRODUCTION WELL. 